Is it acceptable to be lazy during Ramadan?

No one should use the Ramadan fast as an excuse to sleep all day long.

Following a mild and moderate exercise routine is essential to maintain the body active throughout the month, despite feeling sleepy and sluggish during the fasting hours.

A study carried out in Denmark designed to test the impact of fasting and exercise found that exercise induces distinct Growth Hormone (GH) bursts after 30 min. During fasting, more sporadic GH bursts occurred, leading to an overall 3-fold increase in GH. 

GH is a component of the endocrine regulatory system, which is crucial for maintaining lean body mass, growth, and a controlled intermediate metabolism. Acting in tandem with Insulin Growth Factor 1, GH has significant impacts to promote growth and maintain lean body mass protein; some of these anabolic effects are mediated by stimulation of lipolysis. 

Exercise is known to be beneficial to your health, but one thing to keep in mind is that the health condition, type, duration, and  optimum time to work out during Ramadan should be discussed with your doctor beforehand.